Generally a toothbrush has a head and a handle disposed along a longitudinal axis, the head having bristles arranged in tufts extending from a face thereof (“the bristle face”) in a general bristle direction. It is known, e.g. in British Standards Institution publication BS 5757:1979 “Specification for Toothbrushes” that the stiffness of a toothbrush bristle is related to its length and diameter. For bristles of the same diameter and material, longer bristles will be less stiff than shorter bristles.
Generally the bristle face is planar. Toothbrushes are disclosed in inter alia WO 96/25866, GB 1098933, JP-UM-51-129261 and JP-UM-1-155825 in which the bristle face is longitudinally undulating.
Toothbrush bristles are normally mounted on the toothbrush head packed together in tufts. Generally toothbrush bristles are filaments of a polymeric material such as the well known Tynex™ bristles made of nylon, and have a circular cross section. Toothbrush bristles of other cross sections are also known e.g. having a triangular cross section, e.g. see U.S. Pat. No. 4,493,125. Triangular cross section bristles have the advantage that they can penetrate the interproximal spaces between the teeth better than circular section tufts, and also they can be packed together more densely than circular sectioned bristles in a tuft as triangular shapes fit together without the interstitial voids that form between packed circular shapes. However triangular sectioned bristles are generally made of a smaller cross sectional area than circular sectioned bristles so are generally less stiff than circular sectioned bristles of the same length. This can be detrimental to their effectiveness in penetrating the interproximal spaces.
It is an object of the present invention is to provide a construction of toothbrush head which enables the effectiveness of triangular bristles in penetrating the interproximal spaces to be exploited, whilst improving the stiffness of such bristles relative to circular sectioned bristles.